Power Harvesting Scheme Based on Piezoelectricity and Nonlinear Deflections

Abstract

An energy harvesting device (FIG. 1 ) and a method of using the energy harvesting device to generate an electrical charge are described. The energy harvesting device comprises a mass ( 2 ) and at least two tethers ( 4, 6, S and 10 ), at least one of which comprises a piezoelectric material that is mechanically stressable upon deflection of the at least two tethers. Each of the tethers comprises a first end (12) coupled to the mass ( 2 ) and a second end ( 14 ) copied to a reference structure ( 16 ), and the tethers are arranged about the mass such that the mass is moveable within a straight line path relative to the reference. The movement of the mass causes the deflection of the tethers, resulting in the generation of an electric charge. The device is preferably operable at the microscale.

1 - 37 . (canceled) 
     
     
         38 . A wide bandwidth energy harvesting device comprising:
 a proof mass capable of moving in a large deflection amplitude; and   a plurality of tethers arranged around the proof mass to support the proof mass in a center, wherein at least one of the plurality of tethers comprises a piezoelectric material that is mechanically stressable upon deflection of the plurality of tethers, wherein the plurality of tethers are stretchable in response to external vibrations, wherein each of the plurality of tethers has a first end connected to the mass and a second end connected to a reference, and wherein the plurality of tethers are arranged about the proof mass such that the proof mass is moveable within an essentially straightline path relative to the reference;   wherein movement of the proof mass causes the plurality of tethers to deflect and stretch in response to external vibrations, thereby resulting in the generation of an electrical charge.   
     
     
         39 . The energy harvesting device according to  claim 38 , wherein the plurality of tethers are stretchable many times their thickness, thereby stretching the plurality of tethers substantially more than bending the tethers, whereby a large stress is induced. 
     
     
         40 . The energy harvesting device according to  claim 39 , wherein the plurality of tethers are stretchable at least 10 times their thickness. 
     
     
         41 . The energy harvesting device according to  claim 38 , Wherein the plurality of tethers are at least partially covered with a piezoelectric material. 
     
     
         42 . The energy harvesting device according to  claim 41 , wherein the plurality of tethers are covered with a piezoelectric film over at least 80% of the surface of the tether, such that nearly all of the surface area of the plurality of tethers contributes to voltage generation. 
     
     
         43 . The energy harvesting device according to  claim 41 , wherein the piezoelectric material covers a wide middle section of the plurality of tethers. 
     
     
         44 . The energy harvesting device according to  claim 43 , wherein the piezoelectric material does not cover the first end of the tether or the second end of the tether. 
     
     
         45 . The energy harvesting device according to  claim 38 , wherein the proof mass is a polygon and the number of tethers equals the number of sides of the polygon. 
     
     
         46 . The energy harvesting device according to  claim 38 , wherein the operating bandwidth of the energy harvesting device is between about 50 Hz and about 3 kHz. 
     
     
         47 . The energy harvesting device according to  claim 38 , wherein positive and negative deflections of the proof mass generate a large deflection amplitude, wherein said large deflection amplitude is non-resonant. 
     
     
         48 . The energy harvesting device according to  claim 39 , wherein positive and negative deflections of the proof mass generate a large stress on substantially the entire length of each of the plurality of tethers. 
     
     
         49 . The energy harvesting device according to  claim 42 , wherein the stretching of the piezoelectric material is tensile and the charge generated across the piezoelectric material being stretched is of a single polarity. 
     
     
         50 . The energy harvesting device according to  claim 38 , comprising a first cap attachable to the reference and extending over the top surface of the proof mass and a second cap attachable to the reference and extending over the bottom surface of the proof mass, and wherein the first cap and the second cap are spaced from the proof mass to allow the proof mass to move within a straightline path relative to the frame and to prevent over-travel of the proof mass with respect to the reference. 
     
     
         51 . The energy harvesting device according to  claim 50 , wherein the first cap and the second cap comprise a resilient material selected from the group consisting of polydimethylsiloxane, resilient polymers, silicon, silicon coated polymers, and combinations of the foregoing. 
     
     
         52 . The energy harvesting device according to  claim 51 , wherein the proof mass is at least partially covered with a piezoelectric material, whereby impacts of the proof mass with the first cap and the second cap at each deflection extreme generate an electrical charge. 
     
     
         53 . The energy harvesting device according to  claim 38 , comprising means for storing the electrical charge generated by the device. 
     
     
         54 . The energy harvesting device according to  claim 38 , wherein the movement of the proof mass is initiatable by ambient mechanical vibrations. 
     
     
         55 . A method of storing an electrical charge in a wide bandwidth energy harvesting device, the wide bandwidth energy harvesting device comprising a proof mass capable of moving in a large deflection amplitude and a plurality of tethers arranged around the proof mass to support the proof mass in a center, wherein at least one of the plurality of tethers comprises a piezoelectric material that is mechanically stressable upon deflection of the plurality of tethers, wherein the tethers are stretchable in response to external vibrations, and wherein each of the plurality of tethers has a first end connected to the proof mass and a second end connected to a reference, wherein the method comprises the steps of:
 a) subjecting the energy harvesting device to ambient vibrations to move the proof mass in the large deflection amplitude, wherein movement of the proof mass causes the plurality of tethers to deflect and stretch in response to the ambient vibrations, thereby generating an electrical charge; and   b) storing the electrical charge generated by movement of the proof mass.   
     
     
         56 . The method according to  claim 55 , wherein movement of the proof mass in the large deflection amplitude causes the tethers to stretch many times their thickness, whereby a large stress is induced. 
     
     
         57 . The method according to  claim 56 , wherein large positive and negative deflections of the proof mass generate a large stress on substantially the entire length of each of the plurality of tethers. 
     
     
         58 . The method according to  claim 55 , wherein the stretching of the piezoelectric material is tensile and the charge generated across the piezoelectric material being stretched is of a single polarity. 
     
     
         59 . The method according to  claim 55 , wherein the large deflection amplitude is non-resonant. 
     
     
         60 . The method according to  claim 55 , wherein the operating bandwidth of the energy harvesting device is between about 50 Hz and about 3 kHz.